Project Summary of Parent Award Transcription factor RORgt is required for the differentiation of lymphoid cells that not only protect barrier surfaces from infection but also contribute significantly to inflammatory diseases. Using proteomics approaches, we found RORgt to be heavily modified post-translationally (PTM) and interacted with both protein and RNA coregulators. In Th17 cells, RORgt is phosphorylated. To evaluate the implication of these PTMs, we have generated knock- in mice carrying modification-null alleles at the endogenous rorc locus. RORgt target gene expressions were significantly reduced in PTM mutant animals in a cell-type and tissue-specific manner. A more detailed characterization of how RORgt is regulated by different PTMs and their contribution to tissue-specific RORgt interaction partners may provide new approaches for therapeutic intervention in the setting of immunity and autoimmune conditions. In Aim 1, we will first determine if phosphorylation of RORgt helps to facilitate target gene transcription at the level of chromatin accessibility, transcription factor chromatin occupancy, or changes to protein partnership in Th17 cells. In Aim 2, we will determine the role of phosphorylation in RORgt-dependent lymphoid cells in mouse models of multiple sclerosis and colitis. In Aim 3, we will characterize the interaction between MAPK12/p38g and RORgt to determine its contribution to RORgt phosphorylation and transcription activity in Th17 cells. The experiments proposed here in addition to addressing specific mechanistic questions outlined in each Aim, will also lay the groundwork for our long-term goal, to understand how transcription factors achieve cell-type specific functions at the molecular level.